These studies will generate a biologic and immunologic profile for each of several tumor lines studied in order to identify tumor factors or components of the host response which are regularly associated with alterations in antigenic strength. The essence of the proposed study is the use of tumor subline pairs which differ in their antigenic strength as determined by in vivo tumor challenge testing, but which, by virtue of derivation from a common parental tumor line, are likely to be similar in most other biologic characteristics. This approach will eliminate a variety of undefined, usually undetected biologic variables in tumor lines under comparison. It is likely that nonrejection of tumors will be expressed in several ways, affecting immunogenicity, immunosensitivity or both. Each such type of low antigenicity will probably result in a characteristic immunoprofile. Thus, it would be possible to classify tumors in terms of the immunologic relation to their host. Therapeutic approach would differ for each such tumor type, so the ability to classify will provide the minimum basis necessary for decisions concerning immunotherapeutic manipulations.